COLPAERT, JAN V. VERSTUYFT IRIS & VAN ASSCHE JOZEF A.
Laboratorium voor Plantenecologie, Instituut voor Plantkunde, Katholieke Universiteit Leuven, K. Mercierlaan 92, B-3001 Heverlee, BELGIUM.
Ectomycorrhizal roots take up N and P from soil more efficiently
than uncolonized root systems. The external mycelium plays a crucial role in
nutrient acquisition since it increases the soil volume from which nutrients
can be absorbed. We investigated other mechanisms that might improve nutrient
uptake in ectomycorrhizal plants. Kinetics of phosphate and ammonium uptake
and hydrolysis of water soluble organic P by intact ectomycorrhizal and non-mycorrhizal
Pinus sylvestris was studied.
Short term nutrient depletion in solutions circulating over intact root systems
grown in semihydroponics were analysed. Large differences in nutrient uptake
capacity were found between colonized and uncolonized plants of similar size
and nutrient status. Specific uptake rates for ammonium and phosphate were up
to 8 times higher for mycorrhizal root systems. The uptake rates were depended
on the fungus involved and on its developmental stage. Non-mycorrhizal root
systems had lower affinities for Pi and NH4+
uptake than mycorrhizal root systems, although wide variations in Km
values can also be found between the fungal associates themselves. The hydrolysis
of an organic P source by mycorrhizal and non-mycorrhizal pine is illustrated.
Key words: Pinus sylvestris, nutrient uptake kinetics, organic nutrients.